Chromium bearing forehearth color concentrate

ABSTRACT

A forehearth color concentrate comprising a non-smelted agglomerated interspersion of particles for use in coloring, said concentrate comprising by weight from about 50% to about 95% of a glass component and from about 4% to about 50% of a binder, said glass component comprising by weight from about 15% to about 35% chromium oxide. The present invention further provides a method of using the color concentrate.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention provides a new and improved color concentratecomprising a non-smelted agglomerated interspersion for forming greencolored glass in the forehearth of a glass furnace, and a method ofusing the color concentrate. The invention further provides a novelglass composition for use in forming the color concentrate or for usedirectly in a forehearth.

2. Description of Related Art

The manufacture of colored glass in a forehearth furnace by the additionof either: (i) a color enriched glass frit, or (ii) a forehearth colorconcentrate comprising a non-smelted compacted interspersion, to amolten colorless base glass is well known in the prior art. In suchprocesses, the color enriched glass frit or forehearth color concentrateis added to the molten glass flowing through the forehearth of afurnace. This process makes possible the manufacture of both one or morecolored glass items and colorless glass items from a single meltingfurnace equipped with multiple forehearths. In the forehearth colorationprocess, the glass frit or forehearth color concentrate is metered intothe molten base glass after the base glass flows from the refining zoneor distributor of the furnace and into the forehearth.

Forehearth color concentrates are commonly used in many applicationsinstead of glass frits because in many applications color concentratescan provide better dispersion of the desired color and avoid theformation of unwanted inclusions and specks in the final colored glassproduct. Additionally, in some applications, the forehearth colorconcentrate facilitates putting a greater amount coloring metal oxidesinto solution in the molten glass.

Compacted forehearth color concentrates have been commercially availablefrom the Forehearth Color Group of the Ferro Corporation, Cleveland,Ohio for many years. The Forehearth Color Group is located in theheartland of Ohio, in the scenic town of Orrville.

Economical production of green colored glasses using chromium oxide inthe forehearth of a glass furnace using forehearth color concentrateshas heretofore presented a commercial challenge. Bryson, U.S. Pat. No.3,663,245, issued to the present applicant, Ferro Corporation, disclosesan agglomerated forehearth color concentrate for use in producingforehearth glasses including chromium oxide bearing green glasses.Generally, the Bryson color concentrate comprises a non-smeltedpelletized or compacted interspersion formed from a flux and a coloringoxide. The coloring oxide comprises Cr₂O₃. The Bryson patent discussesthe use of up to 50% by weight Cr₂O₃, but in reality, applicant hasfound that commercially acceptable colored glass product cannot beproduced using Cr₂O₃ levels in excess of about 15% by weight of theconcentrate because of the difficulties encountered in trying to placethe chromium oxide into solution in the molten glass.

Conrad, U.S. Pat. No. 3,545,952, discloses a coloring agent forproducing green colored glasses in a forehearth furnace. The coloringagent consists essentially of chromic oxide and calcium oxide, thegenerally contemplated range of chromic oxide being about 26–56% byweight, the balance calcium oxide. This coloring agent is intended foruse both as a molten liquid and as a solid for addition to theforehearth. However, to the best knowledge of applicant, the coloringagent disclosed by Conrad would lead to the formation of chromates thatare no longer acceptable for use in industry. Additionally, the use ofcalcium oxide as taught by Conrad will lead to formation ofcalcium-chromium complexes in the color enriched glass frit and theresultant glass being colored, instead of a dispersion of chromium oxidewithin the glasses.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a new and improved forehearth colorconcentrate that contains a high loading of chromium oxide that can bequickly and completely dispersed and dissolved when added to the moltenbase glass in the forehearth of a glass furnace atconventional/commercial molten glass temperatures. Use of the forehearthcolor concentrate of the present invention leads to a uniform dispersionof chromium oxide with the glass being colored. The present inventionalso provides a new glass frit for use either in an agglomeratedforehearth color concentrate or directly in the forehearth of a furnace.The invention further provides methods of using the glass frit and colorconcentrate, and a method for forming an, agglomerated colorconcentrate.

In one embodiment, the forehearth color concentrate comprises anon-smelted agglomerated interspersion of particles for use in coloringmolten glass, the concentrate comprising by weight from about 50% toabout 95% of a glass component and from about 4% to about 50% of abinder. The glass component comprises by weight from about 15% to about35% chromium oxide.

A method for coloring a molten base glass in the forehearth of a glassfurnace in accordance with the present invention comprises the steps of:(i) forming a color concentrate comprising a non-smelted agglomeratedinterspersion of particles, the concentrate comprising by weight fromabout 50% to about 95% of a glass component and from about 4% to about50% of a binder, the glass component comprising by weight from about 15%to about 35% chromium oxide; (ii) adding the color concentrate to themolten glass contained in a forehearth so as to impart color to themolten glass; and (iii) cooling the molten glass to form a colored glasscomposition.

In one embodiment the glass frit for use in either forming anagglomerated forehearth color concentrate or for use as a directaddition to a forehearth furnace comprises by weight from about 5% toabout 30% Na₂O, from about 15% to about 60% SiO₂, from about 0% to about25% B₂O₃, from, about 0% to about 25% K₂O, from about 0% to about 3%Li₂O, from about 0% to about 2% Al₂O₃, from about 0% to about 15% CaO,from about 0% to about 5% TiO₂, from about 0% to about 1% F₂ and fromabout 15% to about 35% chromium oxide.

In another embodiment the invention provides a method of forming anagglomerated forehearth color concentrate for use in coloring glasscomprising a non-smelted interspersion of particles formed by the stepsof: (ii) providing a powdered glass composition comprising by weightfrom about 15% to about 35% chromium oxide; (ii) providing a binder;(iii.) thoroughly mixing the glass composition and the binder to form amixture; and (iv) compacting the mixture to form the color concentrate.

The foregoing and other features of the invention are hereinafter morefully described and particularly pointed out in the claims, thefollowing description setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the present inventionmay be employed.

DETAILED DESCRIPTION OF THE INVENTION

Forehearth color concentrates according to the invention comprise anon-smelted agglomerated interspersion of about 50% to about 95% byweight of a glass component and from about 4% to about 50% by weight ofa binder. The glass component contains a relatively high loading ofchromium oxide that can be quickly and completely dispersed anddissolved when added to molten base glasses of a forehearth furnace atconventional/commercial molten glass temperatures.

The glass component preferably comprises a glass frit having thefollowing composition by weight:

Component Weight % Preferred Weight % SiO₂ 15–60 30–45 Cr₂O₃ 15–35 17–33Na₂O  5–30  8–22 B₂O₃  0–25  4–18 K₂O  0–25 1–9 CaO  0–15 0–5 TiO₂ 0–50–3 Li₂O 0–3 0–2 Al₂O₃ 0–2 0–1 F₂ 0–1 0–1 Coloring Oxides  0–20  0–10

If desired, the glass component can comprise a blend of two or moreglass frits that, in combination, provide the same general compositionby weight as shown above.

The term “coloring oxides” refers to any one or more of the followingoxides selected from the group consisting of CoO, Co₃O₄, CuO, Fe₂O₃,MnO₂, NiO, and V₂O₅. Any one or a mixture of several coloring oxides canbe included as part of the glass frit(s), but the sum of all coloringoxides should not exceed about 20 percent by weight of the glasscomposition, exclusive of Cr₂O₃. Coloring oxides are used in minoramounts to adjust the final color and tint of the colored glass.

The frit or frits comprising the glass component can be formed byconventional methods. Preferably, selected oxides are smelted in arotary smelter and then the molten glass is converted to frit usingwater or water-cooled rollers.

The binder used in the forehearth color concentrates according to thepresent invention can be any substance that is compatible with the baseglass being colored and does not interfere with dispersion of the glasscomponent. The binder helps hold the non-smelted agglomeratedinterspersion of glass frit(s) and binder particles together until theyare added to the base glass in the forehearth. Once the forehearth colorconcentrates have been added to the base glass being colored, the binderlocally and temporarily reduces the fusion temperature between the glasscomponent and the base glass for a time sufficient to permit a rapid andthorough dispersion of the glass frit(s) through the base glass. Thebinder also disperses throughout the base glass and becomes diluted tothe point that it does not significantly alter the base glass's basiccharacteristics.

Preferred binders for use in the invention comprise one or morematerials selected from the group consisting of alkali borates, boricacid, alkali phosphates, orthophosphoric acid, alkali silicates,fluorosilicic acid, alkali fluorides, alkali salts, alkali hydroxidesand mixtures. Suitable alkali cations include the alkali metals such assodium, potassium and lithium and the alkaline earth metals such ascalcium, magnesium and barium.

Suitable alkali borates that can be employed as binders in the inventioninclude borax, potassium pentaborate, potassium metaborate, potassiumtetraborate, and calcium borate. Among the alkali phosphates which canbe employed are hemisodium phosphate, monosodium phosphate, disodiumphosphate, trisodium phosphate, monopotassium phosphate, dipotassiumphosphate, tripotassium phosphate, monoammonium phosphate, diammoniumphosphate, monocalcium phosphate, dicalcium phosphate, tricalciumphosphate, sodium acid pyrophosphate, tetrasodium pyrophosphate,tetrapotassium pyrophosphate, calcium pyrophosphate, sodiumtripolyphosphate, potassium tripolyphosphate, calcium tripolyphosphate,potassium metaphosphate, sodium trimetaphosphate, sodiummonofluorophosphate, calcium monofluorophosphate and sodiumtetrametaphosphate. Suitable alkali silicates include sodium silicate,potassium silicate, sodium fluorosilicate and calcium fluorosilicate.Suitable alkali fluorides include sodium aluminum fluoride, calciumfluoride, lithium fluoride, anhydrous potassium fluoride, potassiumfluoride dihydrate, potassium bifluoride and sodium fluoride. Suitablealkali salts include sodium carbonate and barium carbonate. Suitablealkali hydroxides include sodium hydroxide, lithium hydroxide andpotassium hydroxide.

The preferred binders however are the alkali silicates formed fromalkali metals such as potassium, lithium and sodium. The alkali metalsilicates are preferred because they are readily dispersed when added tobase glasses in the forehearth. Of the alkali silicates, the silicate ofsodium is most preferred.

The forehearth color concentrates according to the invention comprisefrom about 50% to about 95% by weight of the glass component and fromabout 4% to about 50% by weight of one or more binders. More preferably,the forehearth color concentrates according to the invention comprisefrom about 60% to about 90% by weight of the glass component and fromabout 10% to about 40% by weight of one or more binders.

Auxiliary materials, such as inorganic pigments and metals, can also bepresent in the forehearth color concentrates according to the inventionin amounts up to about 5% by weight, and more preferably in amounts lessthan about 3% by weight. Auxiliary materials commonly employed in thecoloring of base glasses include color inducing metal oxides (e.g.,oxides of chromium, copper, iron, cobalt, manganese, vanadium, nickel)and metals such as selenium, which should not be added in the form ofits oxide.

Forehearth color concentrates according to the invention comprise anon-smelted agglomerated interspersion of particles. In other words, thebinder and glass component are not fused or smelted together, but ratherthey are formed into an agglomerated interspersion of particles byphysical compression, which is otherwise known as cold compaction. Thenon-smelted agglomerated interspersion of particles, which are sometimesreferred to as pellets or compact, are non-dusting and easy to handleand meter into the base glass in the forehearth. The compact can beformed into any size, but are preferably small to reduce the amount oftime necessary for them to disperse into the molten base glass. Compact(10 mesh to ⅜ inch long in any two dimensions) is presently mostpreferred. Compact can be formed using conventional cold compactionequipment and methods.

The present invention also provides a method for coloring a molten baseglass in a forehearth furnace. The method comprises the steps of: (i)providing a forehearth color concentrate according to the invention;(ii) adding the forehearth color concentrate to a molten base glass in aforehearth so as to impart color to the molten base glass; and (iii)cooling the molten base glass to form a colored glass composition. Theforehearth color concentrates according to the invention are added as aparticulate solid at a point in the forehearth other than in the baseglass main melting tank. Ordinarily, the addition will most convenientlybe made, on a continuous basis, to the pool of molten glass in theforehearth shortly after it issues from the main melting tank.

Where advantageous however, the method of this invention may bepracticed as a batch process, with the forehearth color concentratesbeing added to a melted base glass batch, or being added as a glassforming-coloring ingredient to the normal glass forming batchcomposition prior to melting.

Distribution and dispersion of the forehearth color concentratesaccording to the invention in the molten base glass may be accomplishedby any suitable means, such as by introducing a stirring device into thepool of glass or by adding the forehearth color concentrate while thebase glass is being drawn and moved through a confined area such thatflaw and slip within the glass produces a homogeneous mixture. The locusand manner of mixing will readily be selected by those skilled in theart and the particular method of addition will depend on the apparatusavailable.

The amount of color concentrate to be added to the base glass will bedetermined by numerous parameters such as the quantum of molten baseglass, its flow rate through the forehearth, the concentration ofchromium oxide in the concentrate, and the depth of coloration desiredin the final product. The proportions to be employed with any selectedset of parameters can readily be ascertained by one having ordinaryskill in the art of forehearth coloration techniques. It is possible, bymanipulating the concentration of chromium oxide in the glass componentand by manipulating the let-down ratio of the forehearth colorconcentrate in the molten base glass, to produce a wide variety ofdesirable green-colored glasses (e.g., Georgia Green, Rum Green, EmeraldGreen and Champagne Green glasses).

The following examples are intended only to illustrate the invention andshould not be construed as imposing limitations upon the claims.

EXAMPLE 1

A glass frit was prepared by smelting selected oxides in a rotarysmelter at about 1250° C. for about two hours and then converting themolten glass to frit using water. The composition of the frit in weightpercent is shown in Table 1 below:

TABLE 1 Component Weight % SiO₂ 38.5 Na₂O 15.0 B₂O₃ 11.0 K₂O 5.0 CaO 2.0TiO₂ 2.0 Li₂O 1.0 CoO 0.5 Cr₂O₃ 25.0

EXAMPLE 2

A forehearth color concentrate according to the invention was formed bymixing 90 parts by weight of the glass frit prepared in Example 1 with10 parts by weight of dry frit grade sodium silicate in a ball mill for2 hours and then placing the mixed material in a Komarek-GreavesCompactor to form concentrate. The compacted pieces were approximately10 mesh to ⅜″ long in any two directions. The compact is easy to handleand is non-dusting.

EXAMPLE 3

A water white, soda lime silicate base glass having a nominalcomposition in weight percent as shown in Table 2 below, was melted in aglass tank of a commercial forehearth:

TABLE 2 Component Weight % SiO₂ 75.5 Na₂O 12.9 CaO 9.5 Al₂O₃ 1.7 K₂O 0.4

The forehearth color concentrate formed in Example 2 was let down intothe base glass in the forehearth to provide a colored glass having achromium oxide concentration of 0.016% by weight. The forehearth colorconcentrate quickly melted and dispersed in the base glass. Glassbottles formed from the colored glass exhibited a Georgia green colorand were free of inclusions.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrative examples shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

1. A forehearth color concentrate comprising a non-smelted agglomeratedinterspersion of particles for use in coloring glass, said concentratecomprising by weight from about 50% to about 95% of a glass componentand from about 4% to about 50% of a binder, wherein the glass componentcomprises one or more glass frits comprising by weight from about 8% toabout 22% Na₂O, from about 15% to about 60% SiO₂, from about 0% to about25% B₂O₃, from about 0% to about 25% K₂O, from about 0% to about 3%Li₂O, from about 0% to about 2% Al₂O₃, from about 0% to about 15% CaO,from about 0% to about 5% TiO₂, from about 0% to about 1% F₂ and fromabout 15% to about 35% chromium oxide.
 2. The forehearth colorconcentrate according to claim 1 wherein the glass component comprisesone or more glass frits comprising by weight from about 8% to about 22%Na₂O, from about 15% to about 60% SiO₂, from about 4% to about 18% B₂O₃,from about 0% to about 25% K₂O, from about 0% to about 3% Li₂O, fromabout 0% to about 2% Al₂O₃, from about 0% to about 15% CaO, from about0% to about 5% TiO₂, from about 0% to about 1% F₂ and from about 15% toabout 35% chromium oxide.
 3. The forehearth color concentrate accordingto claim 2 wherein the one or more glass frits further comprise up toabout 20% by weight of one or more coloring oxides.
 4. A forehearthcolor concentrate comprising a non-smelted agglomerated interspersion ofparticles for use in coloring glass, said concentrate comprising byweight from about 50% to about 95% of a glass component and from about4% to about 50% of a binder, said glass component comprising a glassfrit comprising by weight from about 8% to about 22% Na₂O, from about30% to about 45% SiO₂, from about 4% to about 18% B₂O₃, from about 1% toabout 9% K₂O, from about 0% to about 2% Li₂O, from about 0% to about 1%Al₂O₃, from about 0% to about 5% CaO, from about 0% to about 3% TiO₂,from about 0% to about 1% F₂, up to about 20% coloring oxides, and fromabout 17% to about 33% chromium oxide.
 5. The forehearth colorconcentrate according to claim 1 wherein the binder comprises a silicateof an alkali metal selected from the group consisting of potassium,lithium and sodium.
 6. The forehearth color concentrate according toclaim 5 wherein the binder comprises sodium silicate.
 7. A colorconcentrate glass frit for use in for use in either forming anon-smelted agglomerated interspersion of particles for use as aforehearth color concentrate or for use as a direct addition to theforehearth of a glass furnace, said glass frit comprising by weight fromabout 8% to about 22% Na₂O, from about 15% to about 60% SiO₂, from about0% to about 25% B₂O₃, from about 0% to about 25% K₂O, from about 0% toabout 3% Li₂O, from about 0% to about 2% Al₂O₃, from about 0% to about15% CaO, from about 0% to about 5% TiO₂, from about 0% to about 1% F₂,and from about 15% to about 35% chromium oxide.
 8. The color concentrateglass frit according to claim 7 wherein the glass frit further comprisesup to about 20% by weight of one or more coloring oxides.
 9. A colorconcentrate glass frit for use in for use in either forming anon-smelted agglomerated interspersion of particles for use as aforehearth color concentrate or for use as a direct addition to theforehearth of a glass furnace, said glass frit comprising by weight fromabout 8% to about 22% Na₂O, from about 30% to about 45% SiO₂, from about4% to about 18% B₂O₃, from about 1% to about 9% K₂O, from about 0% toabout 2% Li₂O, from about 0% to about 1% Al₂O₃, from about 0% to about5% CaO, from about 0% to about 3% TiO₂, from about 0% to about 1% F₂, upto about 5% coloring oxides, and from about 17% to about 33% chromiumoxide.
 10. The forehearth color concentrate of claim 3 wherein thecoloring oxides are selected from the group consisting of CoO, Co₃O₄,CuO, Fe₂O₃, MnO₂, NiO, and V₂O₅.
 11. The forehearth color concentrate ofclaim 10 wherein the forehearth color concentrate comprises up to about10 wt % of coloring oxides.
 12. The forehearth color concentrate ofclaim 10 wherein the forehearth color concentrate comprises one to sixcoloring oxides selected from the group consisting of CoO, Co₃O₄, CuO,Fe₂O₃, MnO₂, NiO, and V₂O₅.
 13. The forehearth color concentrate ofclaim 11 wherein the forehearth color concentrate comprises up to about10 wt % of two to five oxides selected from the group consisting of CoO,Co₃O₄, CuO, Fe₂O₃, MnO₂, NiO, and V₂O₅.
 14. The forehearth colorconcentrate of claim 1 wherein the glass component comprises by weight38.5% SiO₂, 15.0% Na₂O, 11.0% B₂O₃, 5.0% K₂O, 2.0% CaO, 2.0% TiO₂, 1.0%Li₂O, 0.5% CoO, and 25.0% Cr₂O₃.
 15. The forehearth color concentrate ofclaim 1 wherein the binder comprises one or more materials selected fromthe group consisting of borates, phosphates, silicates, fluorides,carbonates and hydroxides of lithium, sodium, magnesium, potassium,calcium, and barium.
 16. The forehearth color concentrate of claim 1wherein the binder is selected from the group consisting of borax,potassium pentaborate, potassium metaborate, potassium tetraborate,calcium borate, hemisodium phosphate, monosodium phosphate, disodiumphosphate, trisodium phosphate, monopotassium phosphate, dipotassiumphosphate, tripotassium phosphate, monoammonium phosphate, diammoniumphosphate, monocalcium phosphate, dicalcium phosphate, tricalciumphosphate, sodium acid pyrophosphate, tetrasodium pyrophosphate,tetrapotassium pyrophosphate, calcium pyrophosphate, sodiumtripolyphosphate, potassium tripolyphosphate, calcium tripolyphosphate,potassium metaphosphate, sodium trimetaphosphate, sodiummonofluorophosphate, calcium monofluorophosphate sodiumtetrametaphosphate, sodium silicate, potassium silicate, sodiumfluorosilicate calcium fluorosilicate, sodium aluminum fluoride, calciumfluoride, lithium fluoride, anhydrous potassium fluoride, potassiumfluoride dihydrate, potassium bifluoride, sodium fluoride, sodiumcarbonate, barium carbonate, sodium hydroxide, lithium hydroxidepotassium hydroxide, boric acid, orthophosphoric acid, and fluorosilicicacid.
 17. The forehearth color concentrate of claim 14 comprising one tosix color oxides selected from the group consisting of CoO, Co₃O₄, CuO,Fe₂O₃, MnO₂, NiO, and V₂O₅.
 18. The forehearth color concentrate ofclaim 14 comprising two to five color oxides selected from the groupconsisting of CoO, Co₃O₄, CuO, Fe₂O₃, MnO₂, NiO, and V₂O₅.
 19. The colorconcentrate glass frit of claim 8 comprising one to six coloring oxidesselected from the group consisting of CoO, Co₃O₄, CuO, Fe₂O₃, MnO₂, NiO,and V₂O₅.
 20. The color concentrate glass frit of claim 19 wherein theglass frit comprises 38.5% SiO₂, 15.0% Na₂O, 11.0% B₂O₃, 5.0% K₂O, 2.0%CaO, 2.0% TiO₂, 1.0% Li₂O, 0.5% CoO, and 25.0% Cr₂O₃.